New Study Shows How Marijuana's Potency Has Changed Over Time

Marijuana has definitely evolved in the last few decades. Its potency is higher than ever: A lab in Colorado has just analyzed 600 samples of marijuana, both recreational and medical, and found that tetrahydrocannabinol (THC) content has risen markedly, whereas cannabidiol (CBD), which many say has therapeutic value, has declined. For all the acceptance that marijuana has gained in recent years – four states allow the sale of pot for recreational use, and 23 states and Washington, DC allow marijuana for medical use – the lack of normalization among marijuana sales may slow the process, since it gives opponents an opening to criticize. Though the results of the new study may be disappointing to some, they're clearly needed, since they show where the market is now and where it needs to go.

The results of the study will be presented this week at a meeting of the American Chemical Society (ACS) in Denver.

DENVER, CO - MARCH 11: A sample of marijuana is in a jar, for customer to look at and smell, at Euflora Dispensary in Denver, March 11, 2015. Colorado pot sales soar to record in January, bringing $2.3 million for schools. Around $36.4 million of recreational marijuana was sold this January compared to about $14.69 million sold the same month last year. (Photo by RJ Sangosti/The Denver Post via Getty Images)

Potency Is Rising

The main finding of the new analysis was that potency has risen by a factor of three in the last few decade. "As far as potency goes, it's been surprising how strong a lot of the marijuana is," says researcher and study lead Andy LaFrate. "We've seen potency values close to 30 percent THC, which is huge.” Potency used to be around 10% or less, but it’s been bred upwards over the years, presumably because the market has demanded it.

The larger surprise from the new analysis is that content may not be so variable, despite what some sellers may advertise. "There's a lot of homogeneity whether you're talking medical or retail level," says LaFrate. "One plant might have green leaves and another purple, and the absolute amount of cannabinoids might change, which relates to strength. But the ratio of THC to CBD to other cannabinoids isn't changing a whole lot.”

Cannabidiol Is Waning

Cannabidiol (CBD) content, on the other hand, has shrunk over time. Researchers have been interested in its use in treating schizophrenia, Huntington's disease, and Alzheimer's disease, among other brain and mood disorders. It’s been said to have antipsychotic effects and to counter the occasionally psychotic effects of THC. So the fact that it’s being bred out may mean that the high one gets from smoking pot isn’t going to vary a lot, despite what sellers may tell you. And it may mean that people who rely on CBD for medicinal properties, aren't getting much of that either.

"There's a lot of homogeneity whether you're talking medical or retail level," says LaFrate. "One plant might have green leaves and another purple, and the absolute amount of cannabinoids might change, which relates to strength. But the ratio of THC to CBD to other cannabinoids isn't changing a whole lot."

Contaminants Are Also Increasing

Finally, the lab tested for contaminants of both the biological and chemical varieties – i.e., anything from microbes to solvents. And the team found a few: "It's pretty startling just how dirty a lot of this stuff is," he says. "You'll see a marijuana bud that looks beautiful. And then we run it through a biological assay, and we see that it's covered in fungi." The team also found butane on some of the samples, which is used to make products like “wax,” an extremely high-potency marijuana.

The biological contaminants aren’t too surprising, since after all, pot is a plant. But contaminants in general may point to the need for some determinations about what’s safe and what’s not. "It's a natural product," LaFrate says. "There's going to be microbial growth on it no matter what you do. So the questions become: What's a safe threshold? And which contaminants do we need to be concerned about?"

What does this actually mean?

The rise in THC content has been going on for years – previous research has also found the same patterns – but the steepness of the rise may be greater than expected. So how much does this affect the general public? That part is up for debate.

“Although the rise in the concentration of THC is not a concern per se, the variability makes it more difficult to titrate the dose to the correct effect,” says Lewis Nelson, Professor and Vice Chair for Academic Affairs at NYU’s Department of Emergency Medicine and Director, of Medical Toxicology Fellowship at the New York City Poison Control Center. “This means that users are more likely to consume excessive doses, leading to adverse clinical effects. This has been seen already in Colorado emergency departments.”

Nora Volkow, Director of the National Institute on Drug Abuse (NIDA) at the National Institutes of Health, agrees that it’s the higher THC content that’s driving the increase in marijuana-related emergency room visits in the country over the last several years. “The higher the THC content, the stronger the effects on the brain,” says Volkow, who's done research on this topic herself. “And the more likely you may end up with toxic reactions – like psychosis. Even the occasional user may end up in the ER. The very significant increase in ER visits – it's due to THC content being much higher now. It’s not that we’ve increased the number of people taking marijuana.”

She adds that the decline in CBD is concerning for medical reasons, since people who legitimately need its therapeutic effects may not be receiving them at all.

The changes in marijuana content may well be worth paying attention to, particularly given the disconnect between what's in the pot and what sellers are saying is in the pot. “Content labeling and dosing instructions would help,” says Nelson, “but accurate information may not be known by the grower or seller, highlighting the inadequate regulatory state of recreational and medical marijuana.”

Knowledge and transparency about what's in marijuana, both recreational and medical, is of utmost importance. Sellers and growers who don’t really know what's in their pot but are telling consumers they do are probably just slowing down the movement. If it's really to move forward, more research and regulation will be key all around.

I fell into writing about health shortly after grad school, where I realized I didn't want to work in a lab for the rest of my life! My main areas of interest are the brain and behavior, as well as what influences the decisions we make about our health, and how we can change...